Particulate detergent compositions of medium to low bulk density may be manufactured by the spray-drying process, or by agglomeration in low shear mixers such as a fluidised bed, or pan granulator and may be used as a "base powder" for a detergent composition. In the spray-drying process, a slurry of components such as anionic detergent active, builder material and optionally nonionic detergent active is manufactured and then dried by spraying it in atomised form into a co- or countercurrent stream of air at high temperature. The resultant particulate compositions may be used directly as a detergent composition or other components can be post-dosed, for example heat or moisture sensitive components, to provide a complete powder composition. The spray-dried granules are found in practice to have bulk densities less than 600 g/l, but the postdosed components may raise the bulk density of the composition to around 700 g/l.
Such low to medium bulk density detergent compositions can be sticky particularly in moist environments and particularly where they have a moderate to high content of organic detergent surfactant. Moderate to high quantities of anionic surfactant can give particular problems. This can make them difficult to handle and process, as they become less free-flowing and tend to form lumps. Such compositions may also have poor storage stability, tending to form cakes on storage, leading to poor product quality.
Particulate composition flow properties can be measured for example by dynamic flow rate and/or the compressibility. Compressibility can be measured by the tests described below. High compressibilities imply poor flow properties. Compositions having in excess of 10% by weight of organic detergent surfactant generally have a compressibility in the range of 20 to 25%. The compressibility of such compositions can under certain conditions be reduced to just above 17%, but further reduction is very difficult without reducing the surfactant level.